Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.
Generally, the motor includes a stator which is secured to the shell of the compressor. The motor rotor rotates within the stator to impart rotation to a crankshaft which is normally press fit within the motor rotor. The crankshaft is rotationally supported by a pair of bearings which are supported by an upper bearing housing and a lower bearing housing. The crankshaft includes an eccentric crank pin which extends into a bore defined in a hub of the orbiting scroll. Disposed between the hub of the crank pin and the inner surface of the bore is a drive bushing which rides against a bearing that is press fit within the bore of the hub.
The hub of the orbiting scroll extends perpendicularly from a base plate of the orbiting scroll. The bore in the hub extends from the open end of the hub to a position generally adjacent the base plate of the orbiting scroll. Thus, the bore in the hub is a blind bore with the open end being positioned at the distal end of the hub and the closed end being positioned at the base plate of the orbiting scroll. During the manufacture of the orbiting scroll, the bore in the hub is machined and the bearing is press fit within the machined bore. Because of the press fit relationship of the bearing and the bore, both the scroll hub and the bearing will deflect during the assembly of the bearing. The total amount of deflection will be determined by the overall stiffness of the hub. The deflection of the hub at the open end of the bore will be greater than the deflection of the hub at the closed end of the bore. The main reason for this unequal deflection is because the hub at the open end of the bore is unsupported while the hub at the closed end of the bore is supported by the end plate. The unequal deflection will result in an assembled bearing having a greater diameter at the open end than at the closed end. This tapered bearing will adversely affect the long term performance of the bearing life and thus the scroll machine.
The present invention presents a solution to the tapered bearing problem by providing a conical bearing bore prior to the installation of the bearing. The conical shape of the bearing bore provides a smaller diameter at the open end and a larger diameter at the closed end. After assembly of the bearing the unequal deflection of the scroll hub will provide an assembled bearing that is more cylindrical than the prior art systems. Thus, the more cylindrical shape will perform longer thus increasing the long term durability of both the bearing and the compressor. The more cylindrical shape increases the durability by providing a uniform clearance between the bearing and the bushing. The uniform clearance increases the load capacity of the bearing due to more uniform pressures being exerted on the bearing. Other advantages include a more uniform press load is required to assemble the bearing and this uniform press load provides a better indication of the holding pressure of the assembly. In addition, the system of the present invention is less sensitive to the dimensional variations of the individual components and this will therefore allow some broadening of the tolerances of the individual dimensions.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.